The equivalent electrical circuit of so-called tight epithelia will be studied by alternating current analysis. Impedance and phase shift will be measured as a function of current frequency, while voltage-divider ratios will be measured with microelectrodes. The data will be fitted to a model whose parameters include the resistances of cell membranes and junctions, the capacitances of cell membranes, and possibly morphological parameters of the cells. BIBLIOGRAPHIC REFERENCES: C. Clausen, S.A. Lewis, J.M. Diamond, and R.S. Eisenberg. Electrical circuit analysis of tight epithelia by alternating current techniques. Biophys. J. 16, 131a (1976). J.M. Diamond. Anion selectivity in biological systems. Fed. Proc. 35, 594 (1976).